Well my reaction has been knee-jerk. Oh shit, still another unwanted unguaranteed change... Sorry for that.
I will not dare to discuss the technical reasons behind such a change which are very probably rock-solid. As I never before experimented USB problems with koreader on my PW3 (I had been told once by a developer whose name I forgot, that the integration of koreader with Kindle was "native", contrary to what happens with Kobo for example), I instinctively felt it was more of a regression than a progress.
This said, I do notice some display improvements. I get less artefacts whan koreader is going out of sleep, if only. On a broader view, it probably concurs to the stability of the software.
I remember using some years ago a small program which could display files seamlessly between kindle and koreader. After some tries, I discarded it because of its instability. Curiously this same instability had never been openly discussed...